INDOCYANINE GREEN - PHYSICOCHEMICAL FACTORS AFFECTING ITS FLUORESCENCE IN-VIVO

This study reinvestigates the spectral properties of ICG (Indocyanine green) in vivo, the role of quenching, and the possibility of an inter action of ICG with blood components and/or vessel walls. ICG quenching as a function of concentration was studied by spectrophotometry on wh ole blood samples from golden hamsters. Fluorescence ICG characteristi cs were evaluated by front-face fluorometry. In vivo, fluorescence mea surements were performed on the femoral artery of golden hamsters. In vitro, on whole blood samples, fluorescence intensity is modified by I CG quenching as concentration increases above 80 mu g/ml. The maximum fluorescence peak is not affected and remains centered at 832 nm. The in vivo measurements display a similar fluorescence intensity shape, w hich is affected only by ICG concentrations. However, the maximum fluo rescence emission peak is modified significantly with time. Between 0 and 120 min, four phases can be distinguished in which a wavelength sh ift from 826 to 835 nm is observed. The wavelength shift with change i n fluorescence intensity observed in vivo could be due to a localizati on of ICG molecules in sites more hydrophobic than serum proteins. It is possible to hypothesize the presence of an endothelium-bound form w ith a specific fluorescence spectrum. The amphiphilic properties of IC G are consistent with fixation of some ICG molecules on sites other th an plasmatic proteins after injection. The process of fixation of ICG molecules on surface components or within the vascular endothelium cou ld be due to a change in the microenvironment of some ICG molecules. ( C) 1998 Academic Press.